I usually will put something under the pad on linear pull brakes. I don't on road caliper brakes. The easiest way for me to get the correct adjustment is to unhook the brake spring on the side you want to adjust. This causes the other spring to pull the pad up against the rim. Having a spacer under the pad, I will gently pull on the brake arm a couple of times while loosely holding onto the pad. This allows the pad and conical washers to adjust themselves to the rim and the spacer. When I am satisfied, I tighten the pad and engage the spring, then move to the other side.

This works well for me, but for some reason others have a hard time with this method. I have tried to teach a few people at the shop and they just don't get how to do it.